The U.S. Justice Department is siding with Qualcomm Inc. /zigman2/quotes/206679220/composite QCOM -0.36% in its bid to hold off enforcement of an antitrust ruling against the chip maker during its appeals process, arguing that the company is important to national security. In documents filed Tuesday, the Justice Department said the district court's ruling "threatens competition, innovation and national security." In a related filing, Ellen Lord, the Defense Department's under secretary for acquisition and sustainment, said "Qualcomm is a key player both in terms of its trusted supply chain and as a leader in innovation, and it would be impossible to replace Qualcomm's critical role in 5G technology in the short term." In May, a federal judge sided with the Federal Trade Commission in ruling that Qualcomm had broken antitrust law through licensing practices that "strangled competition." The San Diego-based company immediately filed an appeal seeking a stay of enforcement, arguing that the ruling would force it to change its business model, which would be too difficult to unwind if the ruling was eventually overturned on appeal.